Characterization of hepatic cation transport is the objective of these studies. Studies are underway to investigate: 1) Normal mechanisms of biliary secretion and hepatic uptake of various cationic compounds using the isolated perfused rat liver and isolated hepatocyte models. Current cationic drugs under investigation include procaine amide ethobromide, propranolol, 1-methyl nicotinamide and glycopyrrolate. Effects of co-administration of various anions and cations and other compounds on these hepatic transport processes are being examined.